To Find The Wavelength of a Sodium Light, By Newton’s Ring.

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LIST OF EXPERIMENT

1. To Determine The Value of “g” By Bar Pendulum and Find The Radius of Gyration.

2. To study Moment of Inertia of a flywheel. 3. To Study the Mass Spring System.

4. To Study The Resolving Power of a Telescope.

5. To Find The Wavelength of a Sodium Light, By Newton’s Ring. 6. To Find The Wavelength of a Sodium Light, By Fresnel’s

Biprism.

7. To Find The Wavelength of Mercury Green Light By Diffraction Grating using

Spectrometer.

8. To Find The Focal Length of Combination of Two Lenses By Nodal Slide

Assembly And Verify The Formula.

9. To Find The Specific Rotation of Cane Sugar By Polarimeter.

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Aim

To Find The Wavelength

of Sodium Light by

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Apparatus Required



_{Optical arrangement for}

Newton’s Rings.



_{Travelling microscope.}



_{Sodium lamp.}



_{Short focus convex lens.}



_{Reading lens.}

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Travelling microscope

A travelling microscope is an instrument for

measuring length with a resolution typically in

the order of 0.01mm .

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Different parts of

Microscope

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Spherometer

Spherometer :- It is a precision

instrument to measure very

small lengths which were

primarily used by

opticians to measure the

curvature of the surface

of a lenses

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Reading Lenses

Reading lenses

Magnifying lenses

used for good

visual correction

And Readability.

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THEORY AND FORMULA USED



_{The wavelength of sodium light is given}

by

:-

_{Where is the diameter of the (m+p)th}

ring and is the diameter of the mth ring .



_{R is the radius of curvature of the convex}

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

_{Hence the determination}

of involves measurement of

radius of curvature of the

surface of lens in contact

with the plate of the glass

and diameter of the two

rings, the difference of their

number being p

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Setting up of crosswire on newton

ring

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Procedure



_{Use a short fixed length lens and place}

it on a plate of glass.



_{The lenses should be placed or}

mounted on a stand such that the rays

fall on the glass plate at 45 to the

vertical.



_{The glass plate p was sending the light}

vertically downwards .

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

_{After obtaining bright fringes , set the}

cross wire at the center of the central

dark ring .



_{Use screw to move the cross wire to the}

twentieth bright ring . Note the readings .



_{Now move the cross wire to nineteenth}

ring.



_{Repeat it till the cross wire to the}

twentieth ring on the left hand side .



_{The radius of curvature of lens is obtained}

with the help of a spherometer.

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OBSERVATIONS

Least count of vernier calipers =

0.01mm

Least count of spherometer =

0.005mm

Spherometer

h =0.15mm

a = 31mm

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Observations

S. NO. RING LEFT

READING (MSR + LC x VSR= TSR) RIGHT READING (MSR + LC x VSR= TSR) DIAMETE R (MM) D2 (MM2₎ 1. 20 51+40x0. 01= 51.40 44+63x0. 01= 44.63 6.77 45.83 2. 19 51+32x0. 01= 51.32 44+81x0. 01= 44.81 6.51 42..38 3. 18 51+16x0. 01= 51.16 44+42x0. 01= 44.42 6.24 38.93 4. 17 51+9x0.0 1 = 51.09 45+9x0.0 1 = 45.09 6.60 36.00 5. 16 50+94x0. 01= 50.94 45+13x0. 01= 45.13 5.81 33.75 6. 15 50+86x0. 01= 50.86 45+25d0. 01= 45.25 5.61 31.47

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11. 10 50+22x0. 01= 50.22 45+81x0. 01= 45.81 4..41 19.44 12. 9 50+10x0. 01= 50.10 45+94x0. 01= 45.94 4..16 12.30 13. 8 49+93x0. 01= 49.93 46+20x0. 01= 46.20 3.73 13.91 14. 7 49+79x0. 01= 49.79 46+30x0. 01= 46.30 3.49 12..18

S. NO. RING LEFT

READING (MSR + LC x VSR= TSR) RIGHT READING (MSR + LC x VSR= TSR) DIAMETE R (MM) D2 (MM2₎ 7. 14 50+71x0. 01= 50.71 45+49x0. 01= 45.49 5.27 28.83 8. 13 50+57x0. 01= 50.57 45+59x0. 01= 45.59 5.08 25.80 9. 12 50+47x0. 01= 50.47 45+71x0. 01= 45.71 4..88 23.81 10. 11 50+33x0. 01= 50.33 45+81x0. 01= 45.81 4..62 21.34

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S.NO. RING LEFT READING (MSR + LC x VSR= TSR) RIGHT READING (MSR + LC x VSR= TSR) DIAMETE R (MM) D2 (MM2₎ 15. 6 49+57x0. 01= 49.57 46+48x0. 01= 46.48 3.09 9.54 16. 5 49+39x0. 01= 49.39 46+65x0. 01= 46.65 2..74 7.78 17. 4 49+18x0. 01= 49.18 46+86x0. 01= 46.86 2..32 5.38 18. 3 48+93x0. 01= 48.93 47+15x0. 01= 47.15 1.78 3.16 19. 2 48+52x0. 01= 48.52 47+55x0. 01= 47.55 0.97 0.94 20. 1 48+42x0. 01= 48.42 47+74x0. 01= 47.74 0.68 0.46

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23

=

10.75mm

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Mean difference of square of diameter

= (14.36 + 13.55 +13.12 +12.41 +11.80 +

11.88 +12.02 + 11.63 + 11.800 +11.66

+6.92 +11.75)/11

=12.38 mm

^(wavelength) =16.20/45106.78

^ (wavelength)= antilog(log16.20 – log20 –

log 1356.64)

= 0.0005796615 * 10

7

A

0

= 5796.61 A

0

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RESULT

Wavelength of sodium light calculated by

Newton’s rings experiment = 5796.96A

0

= (5796.96-5892)*100/5876.97

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APPLICATIONS OF NEWTON’S RINGS

• To measure the refractive index of a substance

placed beneath the same lens.

• To check the thickness of a surface and to check

whether a surface is uniform.

• The interference technique of Newton’s rings is

widely used for the quality control of optical

surfaces because the precision obtained with this

method proves to be very satisfactory. The

dimensions of the permits calculation of the radii of

curvature of the analyzed surfaces and deformation

of the interference pattern can be utilized to

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1. To check thickness of

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2. To measure refractive

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3.Interference technique by

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PRECAUTIONS AND SOURCES OF

ERROR

• The lens should be of large radius of curvature.

• The sources of light used should be an extended

one.

• Before measuring the diameter of the rings , the

range of the microscope should be properly

adjusted.

• Glass plates and lens should be cleaned thoroughly.

• Crosswire should be focused on a bright ring

tangentially.

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BIBLIOGRAPHY

• _{www.google.co.in}

• AK Jha

• _{www.wikipedia.org}

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